Battery build guide ?

[Oily]

Please excuse me if this is arrogant, but although more than happy playing with electrics (I work in IT) I've never got into building (or understanding!) batteries & volts/amps etc.

I've now come to the conclusion that there is no way of (safely) running duall batteries on my EUC, so I'm looking at upgrade options.

Microworks do a 340 (which is a big upgrade from my 132), but it's not cheap & more to the point customs will probably have issues with it even coming into the country !

Is there an idiots guide to making a batter anywhere ?

I've already got a "spare" 132 battery, so presumably I could essentially just upgrade the cells ? 

Do better cells give more Wh, or will I need to increase the number of cells to get more ?

Whats the highest Wh 16 cell battery you can buy/make, as my EUC will only has room for a 16 cell....

Again, sorry for the probably very simple questions !

 

[Oily]

Well, with a bit of googling, I've part answered my own question....

There is a conversion site here : https://milliamps-watts.appspot.com/

So for a 132Wh battery @ 60V, I currently have 22000 mAh.  Divide that by 16 & I have 1375. So the cells I'm currently running are 1375mAh.

Basing a new battery on 3000 cells, I guess my maximum 16 cell battery pack will be : 3000 x 16 = 48000mAh = 288Wh battery.

Looking on eBay, there are claims of 8000 or even 9900mAh cells - but looking on here, but custom build use 3000mAh - are the claims rubbish, or are they just too powerful for an EUC ?

http://www.ebay.co.uk/itm/2x-UltraFire-3-7V-8800mAh-18650-Li-ion-Rechargeable-Battery-Batteries-UK-/262230647066?hash=item3d0e2a211a:g:n8AAAOSwTapV4Z33

[Tomek]

my suggestion, go for high current drain cells like those I've listed here: 

I wouldn't mix old and new batteries in one pack for safety reasons, just buy a BMS from alibaba & make a new pack. e.g. Nkon gives an option to order batteries with U-tags already spot welded on, so that saves some hassle (If the option is not listed on the website, you can call them to enable it for your order)

by the way, your calculations are wrong .') (maximum) current going through the battery is the same whether it's one or 16 batteries in a pack, only voltage changes with the number of cells. 132Wh battery @ 60V means it gives you 2,2Ah = 2200mAh (one zero less), That's ALSO the ampere rating of your individual cells at 3,7V. A battery pack of 3000mAh cells will give you 180Wh (or to be specific 3,7V*16 cells*3Ah = 59,2V*3Ah = 178Wh)

[Keith]

Err... You are having trouble with your maths: P=VxI so 132Wh is 60V x 2,200mAh. So your current batteries are 2.2Ah you don't have to do anything with the 16 cells, each cell is nominally 3.7V so the 16 cells is already allowed for 3.7V x 16 = 59.2V I.e. Your rounded 60V.

a 16 cell 3000mAh battery would be 3000mAh x 59.2V = 177.6Wh. You can get LiPo batteries of 9000mAh but the LiIon 18650 cells used in most wheels can't physically be much more than 3Ah, larger capacity packs use parallel cells. I.e. A 340Wh pack is 16S2P (16 serial, 2 parallel)

Don't forget you need a BMS to balance and protect the batteries as part of any pack.

[Oily]

No plan to mix cells - more a case of use the circuit board from my old battery & weld on new individual cells (or pairs of cells).

I was just using the site in my original post for the conversion - I didn't do any maths !

If I want to build a 340Wh battery (or bigger), how is it done ? Is the only option a 32 cell battery ?

Thanks

[esaj]

AFAIK, the largest 18650-cells available currently are 3500mAh (3.5Ah), like LG MJ1's for example, so you can get around 210Wh max per pack of 16 cells (rounded 60V * 3.5Ah = 210Wh). Larger than that, you need multiple packs (or single pack with more cells wired in parallel). Multiple packs or more cells in parallel are also capable of providing higher power, since the power draw per series is lower (divided among the paralleled cells/packs). So 2 * 100Wh packs would be better than 1 * 200Wh pack in that sense.

Placing cells in series rises the voltage, but the capacity stays the same. Placing cells in parallel, the voltage stays the same, but the capacity rises. The watthours you get is the same in both situations:

16 * 3.7V 2200mAh cells in series (16S1P):  voltage = 16 * 3.7 = 59.2V, capacity = 1 * 2200mAh = 2200mAh (2.2Ah), watthours = 59.2V * 2.2Ah = 130,24Wh (The typical 132Wh value is got using rounded 60V nominal voltage)

16 * 3.7V 2200mAh cells in parallel (1S16P):  voltage = 1 * 3.7 = 3.7V, capacity = 16 * 2200mAh = 35200mAh (35.2Ah), watthours = 3.7V * 35.2Ah = 130,24Wh

Since the motors are built for 60V nominal, you place the cells in series to rise the voltage high enough.

[Keith]

46 minutes ago, Oily said:

If I want to build a 340Wh battery (or bigger), how is it done ? Is the only option a 32 cell battery ?

Simple answer is "Yes" and "No".

No, it isn't the only option, any type of battery including high capacity Radio Control type LiPos can, and have, been used, but you need dedicated chargers and to be absolutely sure what you are doing.

Yes, If you want to stick to hard cased 18650 cells then their physical size limits individual capacity. Some BMS boards are designed so the (tagged) cells are soldered directly to the board so they will limit you to 18650 cells. I believe the 680Wh KingSong uses two parallel 32 cell 16S2P 340Wh packs for example. 

3 hours ago, Oily said:

I've now come to the conclusion that there is no way of (safely) running duall batteries on my EUC

There is absolutely no reason packs cannot be in parallel as long as:

They are the same number of cells in series, I.e. Same nominal voltage, they do not need to be the same capacity, a 16 cell 170Wh pack and 32 cell 16S2P 340Wh pack could be paralleled to make an effective 16S3P pack of 510Wh.

They are both at exactly the same voltage when first connected (prevents high current flowing between packs)

The outputs are connected together and the charging leads are connected together. I'm not convinced that all BMS will allow he approach I've seen some try of daisy chaining output of one pack to the charge connection of the next (I.e. to connect an external piggyback pack.)

It is worth repeating although said many times: there is a hell of a lot of energy in these cells the greatest care is needed not to short circuit or reverse connect cells, check everything multiple times before connecting.

[Oily]

39 minutes ago, Keith said:

Simple answer is "Yes" and "No".

This is awesome - thank you (obviously the full reply) !

I should have clarified, I've got a generic Chinese (might be Huwei) 14" EUC. It's really slimline, so the comment about running twin battery's is more that there isn't the space to physically do it (short of moving the control board outside the main case), as the battery compartment is already tight with a 16cell battery - 32 cells just won't fit in there !

So if I'm understanding this right, this http://wholesaler.alibaba.com/product-detail/Promotion-Electric-self-balance-unicycle-battery_60236130932.html will just be 32 x 3000 cells as a single pack (16SP2).

Hmmmm - this is going to require some more thinking (or LiPo experimentation !) - or a new wheel ! 

[esaj]

22 minutes ago, Oily said:

So if I'm understanding this right, this http://wholesaler.alibaba.com/product-detail/Promotion-Electric-self-balance-unicycle-battery_60236130932.html will just be 32 x 3000 cells as a single pack (16SP2).

Yes, there are 2 sets of 16 cells on top of each other (partially overlapping between each other, so it's a bit thinner than two separate 16S1P's, but not much) inside. Probably over 30mm or more thickness with the BMS.

 

 

EDIT: Actually they state the size there:    159x143x38 mm